Hydrogels have long been of interest for biological and biomaterial applications due to their high water content that mimics the interstitial tissue environment, ensures high diffusive permeability, and provides biomimetic mechanical strengths. Particular interest has been given to PEG hydrogels and poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogels because, in addition to the general properties of hydrogels, they are also commonly considered to be low fouling, bioinert, and versatile.
pHEMA hydrogels have found use in and been studied for applications such as contact lenses, artificial cornea, drug delivery vehicles, cartilage substitutes, and tissue scaffolds, among others. The hydration of pHEMA, however, is lower than that of native tissue, and its fouling, while low, is higher than other nonfouling materials. Furthermore, pHEMA functionalization via the hydroxyl group is generally difficult.
PEG hydrogels are routinely used, and can only be modified for applications that require a bioinert background with specific added bioactive functionalities for controlled in vitro and in vivo uses when additional functional groups are introduced into PEG hydrogels. However, it has been found that PEG is susceptible to oxidation. The susceptibility of PEG to oxidative damage reduces its utility for applications that require long-term material stability. For applications in which maximal biological stability and nonfouling are required, however, PEG-based materials are insufficient.
Recently, zwitterionic compounds, including poly(carboxybetaine methacrylate), have been demonstrated to be ultra-low-fouling, meaning that surfaces coated with these polymers allow less than 5 ng/cm2 protein adsorption. Because of the high hydration and ultralow fouling properties of zwitterionic materials, zwitterionic hydrogels are of interest as hydrogels with superior suitability for biomedical applications. The zwitterionic hydrogels studied so far, however, have shown low mechanical strength, which limits their potential biological uses.
A need therefore exists for hydrogels having improved mechanical properties. The present invention seeks to fulfill this need and provides further related advantages.